It is known that the rate of chemical reactions can be accelerated to decrease reaction times by several orders of magnitude by using microwave energy, provided the reaction medium includes at least one solvent or reactant having a high dielectric loss tangent so as to couple effectively with the microwaves. Such accelerated reaction times, however, usually involve the generation of high temperatures and pressures, particularly in sealed reaction vessels, and there exists a need to provide effective reaction monitoring, control and safety facilities on the microwave heating equipment.
The applicant's prior International Application No. PCT/AU89/00437 (Publication No. WO 90/03840) discloses a laboratory flow-through unit for conducting microwave initiated chemical reactions on a continuous basis which incorporates reaction monitoring and control facilities. However, the monitoring and control facilities on this known unit are located outside the microwave irradiation zone. Furthermore, this known unit does not meet laboratory applications that are not suited to continuous processes.
Apparatus for performing chemical reactions on a batch basis that includes facilities to monitor temperature and pressure within the reaction vessel is disclosed by D. Constable, K. Raner, P. Somlo and C. Strauss in the article "A New Microwave Reactor Suitable for Organic Synthesis and Kinetics Studies", Journal of Microwave Power and Electromagnetic Energy, Vol. 27 No. 4, 1992, pages 195-198 (the disclosure of which is incorporated herein by cross-reference). In this reactor, a reaction vessel having a screw-cap lid with pressure and temperature monitoring fittings, is situated within a microwave cavity. The reaction vessel also contains a stirrer bar, which is magnetically driven from outside the microwave cavity.
Although the Constable et al. reactor includes facilities to monitor reaction conditions within the microwave irradiation zone, its only controllable input is the power level of the microwaves. Thus in the Constable et al. reactor it is not possible, for example, to controllably cool the reaction products nor to add or subtract from the vessel's contents during the course of a reaction.